Shutter device and image pickup apparatus including shutter device

ABSTRACT

When a stepping motor is used as a driving source for a shutter device, if the stepping motor loses synchronization because of variations in load during driving or the like, it becomes unable to rotate a driving ring at that time, and this disables an exposure operation. In a first zone where a driven member is driven, but a light shielding member remains in a closed state or an open state, the motor drives the driven member in open-loop driving mode. In a second zone where the driven member is driven, and thus the light shielding member moves to the closed state or the open state, the motor drives the driven member in feed-back driving mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/538,055 filed Nov. 11, 2014, which claims the benefit ofInternational Patent Application No. PCT/JP2013/080757, filed Nov. 14,2013, all of which are hereby incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present invention relates to a shutter device and an image pickupapparatus including the shutter device.

BACKGROUND ART

Patent Literature 1 discloses a shutter device in which two shutterblades are made to open or close an opening portion by a stepping motorrotating a driving ring.

The shutter device disclosed in Patent Literature 1 has an accelerationregion where the driving ring is rotated, but the two shutter blades donot open or close the opening portion and an exposure region where thetwo shutter blades are made to open or close the opening portion byrotation of the driving ring. In the shutter device disclosed in PatentLiterature 1, after the stepping motor is accelerated in theacceleration region, the two shutter blades open or close the openingportion in the exposure region.

CITATION LIST Patent Literature

PTL 1 Japanese Patent Laid-Open No. 7-56211

For the shutter device disclosed in Patent Literature 1, in the exposureregion, a load for moving the two shutter blades may cause the steppingmotor to lose synchronization.

That is, when the stepping motor is used as a driving source for thestepping motor, if the stepping motor loses synchronization because ofvariations in load during driving, it becomes unable to rotate thedriving ring at that time, and this disables an exposure operation.

It is an object of the present invention to provide a shutter device inwhich, when a stepping motor drives a driven member and thus a lightblocking member moves from a closed state to an open state or from theopen state to the closed state, the stepping motor does not losesynchronization.

SUMMARY OF INVENTION

A shutter device according to an aspect of the present inventionincludes a stepping motor, a driven member, and a light shieldingmember. The stepping motor is configured to be driven in open-loopdriving mode at which an energization state of a coil is switched atpredetermined time intervals and in feed-back driving mode at which theenergization state of the coil is switched in accordance with a rotationposition of a rotor. The driven member is configured to be driven by thestepping motor. The light shielding member is configured to move to aclosed state in which an aperture is closed and to an open state inwhich the aperture is open in coordination with driving the drivenmember. The driven member is configured to be driven in a first zonewhere the driven member is driven by the stepping motor, but the lightshielding member remains in the closed state or the open state and in asecond zone where the driven member is driven by the stepping motor, andthus the light shielding member moves from the closed state to the openstate or from the open state to the closed state. The driven member isdriven in the first zone by the stepping motor in one direction, andafter the driven member is driven in the first zone, the driven memberis driven in the second zone. In a case where the driven member isdriven in the first zone, the stepping motor drives the driven member inthe open-loop driving mode. In a case where the driven member is drivenin the second zone, the stepping motor drives the driven member in thefeed-back driving mode.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are illustrations for describing a shutter unit 20 as ashutter according to one embodiment of the present invention.

FIG. 2 is an illustration of a first rotor plate 107 (second rotor plate117) as seen from a back surface side.

FIGS. 3A and 3B are illustrations for describing a state of the shutterunit 20 in A status.

FIGS. 4A and 4B are illustrations for describing a state of the shutterunit 20 in B status.

FIGS. 5A and 5B are illustrations for describing a state of the shutterunit 20 in C status.

FIGS. 6A and 6B are illustrations for describing a state of the shutterunit 20 in D status.

FIGS. 7A and 7B are illustrations for describing a state of the shutterunit 20 in E status.

FIGS. 8A and 8B are illustrations for describing a state of the shutterunit 20 in F status.

FIGS. 9A and 9B are illustrations for describing a state of the shutterunit 20 in G status.

FIGS. 10A and 10B are illustrations for describing a state of theshutter unit 20 in H status.

FIGS. 11A and 11B are illustrations for describing a state of theshutter unit 20 in I status.

FIG. 12 is a timing chart for describing operations of the shutter unit20 when a camera 100 is operating in continuous shooting mode.

FIG. 13 is a timing chart for describing operations of the shutter unit20 when the camera 100 is operating in continuous shooting mode as avariation of the embodiment.

FIG. 14 illustrates a motor 1 used as each of a first motor Ma and asecond motor Mb.

FIGS. 15A to 151 are illustrations for describing operations of themotor.

FIGS. 16A to 16D are illustrations for describing positions in which afirst magnetic sensor 8, a second magnetic sensor 9, a third magneticsensor 10, and a fourth magnetic sensor 11 are arranged.

FIG. 17 is a central sectional view of the digital single-lens reflexcamera body 100 as an image pickup apparatus according to one embodimentof the present invention and an interchangeable lens 50.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described in detail below withreference to the drawings.

FIG. 17 is a central sectional view of a digital single-lens reflexcamera body (hereinafter referred to as camera) 100 according to oneembodiment of the present invention and an interchangeable lens 50 as animage pickup apparatus.

The interchangeable lens 50 is detachably fixed on the camera 100 with amount section 210 in the camera 100 and a mount section 51 in theinterchangeable lens 50. When the interchangeable lens 50 is attached tothe camera 100, a contact section 220 in the camera 100 and a contactsection 52 in the interchangeable lens 50 are electrically connected toeach other.

A light flux that has passed through focus lenses 53 in theinterchangeable lens 50 enters a main mirror 130 in the camera 100. Themain mirror 130 is held on a main mirror holding frame 131 and issupported by a rotating shaft section 131 a so as to be able to pivotbetween a mirror upper position and a mirror lower position.

The main mirror 130 is a semitransparent mirror. A light flux that haspassed through the main mirror 130 is reflected downward by a sub mirror140 and is guided to a focus detecting unit 150.

The sub mirror 140 is held on a sub mirror holding frame 141. The submirror holding frame 141 is supported by a hinge shaft (not illustrated)so as to be able to pivot with respect to the main mirror holding frame131.

The focus detecting unit 150 is configured to detect the amount ofdefocusing of the focus lenses 53 and calculate the amount of driving ofthe focus lenses 53 for achieving focus for the focus lenses 53. Theinterchangeable lens 50 is configured to receive the calculated amountof driving through the contact sections 220 and 52. The interchangeablelens 50 is configured to adjust the focus by controlling a motor (notillustrated) and driving the focus lenses 53 on the basis of thereceived amount of driving.

A light flux reflected by the main mirror 130 is guided to an opticalviewfinder 160. The optical viewfinder 160 includes a focusing plate170, a pentaprism 180, and an eyepiece 190. The light flux guided to theoptical viewfinder 160 forms an object image on the focusing plate 170.A user can observe the object image on the focusing plate 170 throughthe pentaprism 180 and the eyepiece 190.

A shutter unit 20 is arranged behind the sub mirror 140. An opticallow-pass filter 21, an image pickup element holder 22, an image pickupelement 23, a cover member 24, and a rubber member 25 are arrangedbehind the shutter unit 20. In shooting, a light flux that has passedthrough the optical low-pass filter 21 enters the image pickup element23. The image pickup element holder 22 is fixed to the housing of thecamera 100 with a screw (not illustrated). The image pickup element 23is held by the image pickup element holder 22. The cover member 24protects the image pickup element 23. The rubber member 25 holds theoptical low-pass filter 21 and hermetically seals the gap between theoptical low-pass filter 21 and the image pickup element 23.

A display monitor 26 may be a liquid crystal display monitor and isconfigured to display a shot image and display various setting statusesof the camera 100.

FIGS. 1A and 1B are illustrations for describing the shutter unit 20 asa shutter according to one embodiment of the present invention. FIG. 1Ais an exploded perspective view for describing a configuration of theshutter unit 20. FIG. 1B is an exploded perspective view illustratingthe shutter unit 20 further disassembled from the state illustrated inFIG. 1A.

As illustrated in FIG. 1A, the shutter unit 20 is driven by a firstmotor Ma and a second motor Mb. The first motor Ma is connected to adriving circuit 14 a. The second motor Mb is connected to a drivingcircuit 14 b. The driving circuit 14 a and the driving circuit 14 b areconnected to a control circuit 13. In the present embodiment, the firstmotor Ma and the second motor Mb are the same motors. A pinion gear 101is press-fit to the output shaft of the first motor Ma. A pinion gear111 is press-fit to the output shaft of the second motor Mb.

The first motor Ma is mounted to a motor mounting plate 102. The motormounting plate 102 is fixed to a cover plate 103. The second motor Mb ismounted to a motor mounting plate 112. The motor mounting plate 112 isfixed to a cover plate 113.

A driving mechanism accommodating section 104 accommodates a first rotorplate 107 to which a weight 106 is bonded and a second rotor plate 117to which a weight 116 is bonded. The first rotor plate 107 includes aprotruding section 107 a. When the cover plate 103 is mounted on thedriving mechanism accommodating section 104, the protruding section 107a is exposed through the cover plate 103. The second rotor plate 117includes a protruding section 117 a. When the cover plate 113 is mountedon the driving mechanism accommodating section 104, the protrudingsection 117 a is exposed through the cover plate 113. A first spring 108is mounted to the cover plate 103. A second spring 118 is mounted to thecover plate 113.

The first rotor plate 107 includes a gear section 107 b. When the motormounting plate 102 is fixed on the cover plate 103, the pinion gear 101and the gear section 107 b engage with each other. The second rotorplate 117 includes a gear section 117 b. When the motor mounting plate112 is fixed on the cover plate 113, the pinion gear 111 and the gearsection 117 b engage each other.

Accordingly, when the first motor Ma is driven, the first rotor plate107 rotates; when the second motor Mb is driven, the second rotor plate117 rotates.

A blade accommodating section 105 has an aperture 105 a. The bladeaccommodating section 105 accommodates a first blade 110 and a secondblade 120.

As illustrated in FIG. 1B, a driving arm 110 a is mounted to the firstblade 110. A driving arm 120 a is mounted to the second blade 120.

A first driving lever 109 and a second driving lever 119 are supportedon the driving mechanism accommodating section 104. The first drivinglever 109 includes a cam pin 109 a and an engagement pin 109 b. The campin 109 a engages with a cam groove 107 c in the first rotor plate 107.The engagement pin 109 b engages with the driving arm 110 a. When thefirst driving lever 109 pivots, the first blade 110 opens or closes theaperture 105 a. Similarly, the second driving lever 119 includes a campin 119 a and an engagement pin 119 b. The cam pin 119 a engages with acam groove 117 c in the second rotor plate 117. The engagement pin 119 bengages with the driving arm 120 a. When the second driving lever 119pivots, the second blade 120 opens or closes the aperture 105 a. In thepresent embodiment, the first driving lever 109 and the second drivinglever 119 are the same components.

The driving mechanism accommodating section 104 includes a shaft section104 a and a shaft section 104 b. The first rotor plate 107 is supportedby the shaft section 104 a. The second rotor plate 117 is supported bythe shaft section 104 b. The first rotor plate 107 includes the gearsection 107 b on its front surface. The weight 106 is bonded and fixedto the circumferential section of the first rotor plate 107. The firstrotor plate 107 includes the cam groove 107 c, with which the cam pin109 a engages, in its back surface.

Similarly, the second rotor plate 117 includes the gear section 117 b onits front surface. The weight 116 is bonded and fixed to thecircumferential section of the second rotor plate 117. The second rotorplate 117 includes the cam groove 117 c, with which the cam pin 119 aengages, in its back surface. In the present embodiment, the first rotorplate 107 and the second rotor plate 117 are the same components. Theweight 106 and the weight 116 are the same components.

Each of the first rotor plate 107 and the second rotor plate 117functions as a driven member. The first blade 110 and the first drivinglever 109 function as a light shielding member capable of moving betweena closed state where they closes the aperture 105 a and an open statewhere they opens the aperture 105 a in coordination with driving thefirst rotor plate 107. The second blade 120 and the second driving lever119 function as a light shielding member capable of moving between aclosed state where they closes the aperture 105 a and an open statewhere they opens the aperture 105 a in coordination with driving thesecond rotor plate 117. Each of the first spring 108 and the secondspring 118 functions as an urging member.

FIG. 2 is an illustration of the first rotor plate 107 (second rotorplate 117) as seen from the back surface side. The cam groove 107 c (camgroove 117 c), with which the cam pin 109 a (cam pin 119 a) engages, aredisposed in the back surface of the first rotor plate 107 (second rotorplate 117). As illustrated in FIG. 2, a first idle running drivingregion A, an exposure driving region B, and a second idle runningdriving region C are set in the cam groove 107 c (cam groove 117 c). Inthe first idle running driving region A and the second idle runningdriving region C in the cam groove 107 c (cam groove 117 c), the camlift is substantially zero.

When the cam pin 109 a (cam pin 119 a) follows the first idle runningdriving region A or the second idle running driving region C, the firstdriving lever 109 (second driving lever 119) does not rotate and thefirst blade 110 (second blade 120) remains in a closed state or an openstate.

When the cam pin 109 a (cam pin 119 a) follows the exposure drivingregion B, the first driving lever 109 (second driving lever 119) rotatesand the first blade 110 (second blade 120) moves from the closed stateto the open state or from the open state to the closed state.

When the first rotor plate 107 (second rotor plate 117) rotatesclockwise, the cam pin 109 a (cam pin 119 a) follows the first idlerunning driving region A, the exposure driving region B, and the secondidle running driving region C in this order.

The details of the clockwise rotation of the first rotor plate 107(second rotor plate 117) are described below.

The first idle running driving region A is a first cam region. The zonewhere the cam pin 109 a (cam pin 119 a) follows the first idle runningdriving region A is a first zone.

The exposure driving region B is a second cam region. The zone where thecam pin 109 a (cam pin 119 a) follows the exposure driving region B is asecond zone.

The second idle running driving region C is a third cam region. The zonewhere the cam pin 109 a (cam pin 119 a) follows the second idle runningdriving region C is a third zone.

In contrast, when the first rotor plate 107 (second rotor plate 117)rotates counterclockwise, the cam pin 109 a (cam pin 119 a) follows thesecond idle running driving region C, the exposure driving region B, andthe first idle running driving region A in this order.

The details of the counterclockwise rotation of the first rotor plate107 (second rotor plate 117) are described below.

The second idle running driving region C is the first cam region. Thezone where the cam pin 109 a (cam pin 119 a) follows the second idlerunning driving region C is the first zone.

The exposure driving region B is the second cam region. The zone wherethe cam pin 109 a (cam pin 119 a) follows the exposure driving region Bis the second zone.

The first idle running driving region A is the third cam region. Thezone where the cam pin 109 a (cam pin 119 a) follows the first idlerunning driving region A is the third zone.

That is, the first rotor plate 107 (second rotor plate 117) is driven inone direction, and thus the first rotor plate 107 (second rotor plate117) is driven in the first zone. After the first rotor plate 107(second rotor plate 117) is driven in the first zone, the first rotorplate 107 (second rotor plate 117) is driven in the second zone.

As illustrated in FIG. 1B, the cover plate 103 is provided with a hollowshaft section 103 a. When the cover plate 103 is mounted on the drivingmechanism accommodating section 104, the protruding section 107 a in thefirst rotor plate 107 is exposed through the cover plate 103 and theshaft section 104 a is fit into an inner section of the hollow shaftsection 103 a. The first spring 108 is mounted on an outer section ofthe hollow shaft section 103 a.

Similarly, the cover plate 113 is provided with a hollow shaft section113 a. When the cover plate 113 is mounted on the driving mechanismaccommodating section 104, the protruding section 117 a in the secondrotor plate 117 is exposed through the cover plate 113 and the shaftsection 104 b is fit into an inner section of the hollow shaft section113 a. The second spring 118 is mounted on an outer section of thehollow shaft section 113 a.

When the motor mounting plate 102 with the first motor Ma mountedthereon is mounted on the cover plate 103, the output shaft of the firstmotor Ma penetrates through an opening in the cover plate 103, and thepinion gear 101 and the gear section 107 b engage with each other.Similarly, when the motor mounting plate 112 with the second motor Mbmounted thereon is mounted on the cover plate 113, the output shaft ofthe second motor Mb penetrates through an opening in cover plate 113,and the pinion gear 111 and the gear section 117 b engage with eachother.

In the present embodiment, the first motor Ma, the first rotor plate107, the first spring 108, the first driving lever 109, and the firstblade 110 constitute a first shutter driving mechanism. The second motorMb, the second rotor plate 117, the second spring 118, the seconddriving lever 119, and the second blade 120 constitute a second shutterdriving mechanism.

Each of the first motor Ma and the second motor Mb is a stepping motorthat can be driven in step-driving (open-loop driving) at which anenergization state of the coil is switched at predetermined timeintervals and in two types of feed-back driving with different advanceangle values. To drive the first motor Ma and the second motor Mb in thestep driving mode (open-loop driving mode), the energization state ofthe coil is switched at predetermined time intervals. To drive the firstmotor Ma and the second motor Mb in the feed-back driving mode, theenergization state of the coil is switched in accordance with an outputof a positional sensor.

The detailed configuration of each of the first motor Ma and the secondmotor Mb is described below.

FIG. 12 is a timing chart for describing operations of the shutter unit20 when the camera 100 is operating in continuous shooting mode. FIGS. 3to 11 are illustrations for describing the states of the shutter unit 20in A to I statuses illustrated in FIG. 12.

The shutter unit 20 according to the present embodiment performs afirst-frame shooting operation from the A status to H status illustratedin FIG. 12. In the first-frame shooting operation, the first shutterdriving mechanism functions as a leading blade, and the second shutterdriving mechanism functions as a trailing blade. The shutter unit 20according to the present embodiment performs a second-frame shootingoperation from the H status to I status illustrated in FIG. 12. In thesecond-frame shooting operation, the second shutter driving mechanismfunctions as the leading blade, and the second shutter driving mechanismfunctions as the trailing blade. In a third-frame shooting operation,the first shutter driving mechanism functions as the leading blade, andthe second shutter driving mechanism functions as the trailing blade.

When the camera 100 starts a shooting operation, it is in A statusillustrated in FIG. 12. FIGS. 3A and 3B are illustrations for describinga state of the shutter unit 20 in A status. FIG. 3A is an illustrationfor describing the state of the first shutter driving mechanism. FIG. 3Bis an illustration for describing the state of the second shutterdriving mechanism.

As illustrated in FIG. 3A, in A status, the first blade 110 closes theaperture 105 a. In the state illustrated in FIG. 3A, the protrudingsection 107 a in the first rotor plate 107 is in contact with the leftarm section of the first spring 108. However, in this state, the firstspring 108 is not charged and is in its natural state.

As illustrated in FIG. 3B, in A status, the second blade 120 opens theaperture 105 a. At this time, the protruding section 117 a in the secondrotor plate 117 is in contact with the right arm section of the secondspring 118. However, in this state, the second spring 118 is not chargedand is in its natural state.

As illustrated in FIG. 12, in A status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivenclockwise in feed-back driving mode with low advance angle. In A status,the control circuit 13 controls the driving circuit 14 b such that thesecond motor Mb is not driven in any direction. Thus the shutter unit 20moves to the B status illustrated in FIG. 12.

FIGS. 4A and 4B are illustrations for describing a state of the shutterunit 20 in B status. FIG. 4A is an illustration for describing the stateof the first shutter driving mechanism. FIG. 4B is an illustration fordescribing the state of the second shutter driving mechanism.

As illustrated in FIG. 4A, in B status, the first blade 110 closes theaperture 105 a. As illustrated in FIG. 12, in the period from the Astatus to B status, the first motor Ma is driven clockwise in feed-backdriving mode with low advance angle. Thus the first rotor plate 107rotates counterclockwise from the state illustrated in FIG. 3A. Here,because the pinion gear 101 in the first motor Ma and the gear section107 b in the first rotor plate 107 engage with each other, the rotationdirection of the first motor Ma and that of the first rotor plate 107are opposite.

When the first rotor plate 107 rotates counterclockwise from the stateillustrated in FIG. 3A (A status), the first rotor plate 107 rotateswhile charging the first spring 108. In this period, the first rotorplate 107 rotates counterclockwise while charging the first spring 108,and thus variations in load during the driving of the first motor Ma arelarge. However, because the first motor Ma is driven in feed-backdriving mode with low advance angle, the first motor Ma does not losesynchronization.

In the state illustrated in FIG. 4A (B status), because the first spring108 is charged, the first rotor plate 107 is urged in a clockwisedirection by the first spring 108.

When the first rotor plate 107 rotates counterclockwise from the stateillustrated in FIG. 3A (A status), the cam pin 109 a in the firstdriving lever 109 follows the first idle running driving region A in thecam groove 107 c in this period. Accordingly, the position of the firstdriving lever 109 in the state illustrated in FIG. 4A (B status) issubstantially the same as the position of the first driving lever 109 inthe state illustrated in FIG. 3A (A status).

The B status of the second shutter driving mechanism illustrated in FIG.4B is the same as the A status of the second shutter driving mechanismillustrated in FIG. 3B. When the state moves from the A status to Bstatus, the second motor Mb is not driven, and thus the second rotorplate 117 remains unchanged from the state illustrated in FIG. 3B (Astatus).

As illustrated in FIG. 12, in B status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivencounterclockwise in step driving mode. In B status, the control circuit13 controls the driving circuit 14 b such that the second motor Mb isdriven clockwise in feed-back driving mode with low advance angle. Thusthe shutter unit 20 moves to the C status illustrated in FIG. 12. Thatis, in the present embodiment, the start of driving for an approach runin the second shutter driving mechanism lags behind the start of drivingfor an approach run in the first shutter driving mechanism by anexposure time t1.

The first shutter driving mechanism starts driving for an approach runin step driving mode in B status. In driving for the approach run, thecontrol circuit 13 gradually increases the rotational speed of the firstmotor Ma by gradually reducing the width of a driving pulse. In drivingfor the approach run, the cam pin 109 a follows the first idle runningdriving region A in the cam groove 107 c, where the cum lift issubstantially zero. Accordingly, in this period, because the firstdriving lever 109 does not virtually rotate even when the first rotorplate 107 is driven, variations in load during the driving of the firstmotor Ma are small. Thus when the first motor Ma is driven in stepdriving mode, the first motor Ma does not lose synchronization.

FIGS. 5A and 5B are illustrations for describing a state of the shutterunit 20 in C status. FIG. 5A is an illustration for describing the stateof the first shutter driving mechanism. FIG. 5B is an illustration fordescribing the state of the second shutter driving mechanism.

As illustrated in FIG. 5A, in C status, the first blade 110 closes theaperture 105 a. Because the first motor Ma is driven counterclockwise inthe period from the B status to C status, the first rotor plate 107 isrotated clockwise by a combined force of the driving force of the firstmotor Ma and the urging force of the first spring 108. The urging forceof the first spring 108 is provided to the first rotor plate 107 up tothe C status illustrated in FIG. 5A.

When the first rotor plate 107 rotates clockwise from the stateillustrated in FIG. 4A (B status), the cam pin 109 a in the firstdriving lever 109 follows the first idle running driving region A in thecam groove 107 c in this period. Accordingly, the position of the firstdriving lever 109 in the state illustrated in FIG. 5A (C status) issubstantially the same as the position of the first driving lever 109 inthe state illustrated in FIG. 4A (B status).

As illustrated in FIG. 5B, in C status, the second blade 120 opens theaperture 105 a. In the period from the B status to C status, because thesecond motor Mb is driven clockwise in feed-back driving mode with lowadvance angle, the second rotor plate 117 rotates counterclockwise fromthe state illustrated in FIG. 4B. Here, because the pinion gear 111 inthe second motor Mb and the gear section 117 b in the second rotor plate117 engage with each other, the rotation direction of the second motorMb and that of the second rotor plate 117 are opposite.

When the second rotor plate 117 rotates clockwise from the stateillustrated in FIG. 4B (B status), the second rotor plate 117 rotateswhile charging the second spring 118. In this period, the second rotorplate 117 rotates clockwise while charging the second spring 118, andthus variations in load during the driving of the second motor Mb arelarge. However, because the second motor Mb is driven in feed-backdriving mode with low advance angle, the second motor Mb does not losesynchronization.

In the state illustrated in FIG. 5B (C status), because the secondspring 118 is charged, the second rotor plate 117 is urged in aclockwise direction by the second spring 118.

When the second rotor plate 117 rotates clockwise from the stateillustrated in FIG. 4B (B status), the cam pin 119 a in the seconddriving lever 119 also follows the first idle running driving region Ain the cam groove 117 c in this period. Accordingly, the position of thesecond driving lever 119 in the state illustrated in FIG. 5B (C status)is substantially the same as the position of the second driving lever119 in the state illustrated in FIG. 4B (B status).

As illustrated in FIG. 12, in C status, the control circuit 13 alsocontrols the driving circuit 14 a such that the first motor Ma is drivencounterclockwise in step driving mode. In C status, the control circuit13 controls the driving circuit 14 b such that the second motor Mb isdriven counterclockwise in step driving mode. Thus the shutter unit 20moves to the D status illustrated in FIG. 12. The second shutter drivingmechanism starts driving for an approach run in step driving mode in Cstatus. In driving for the approach run, the control circuit 13gradually increases the rotational speed of the second motor Mb bygradually reducing the width of a driving pulse. In driving for theapproach run, the cam pin 119 a follows the first idle running drivingregion A in the cam groove 117 c, where the cum lift is substantiallyzero. Thus when the second motor Mb is driven in step driving mode, thesecond motor Mb does not lose synchronization.

FIGS. 6A and 6B are illustrations for describing a state of the shutterunit 20 in D status. FIG. 6A is an illustration for describing the stateof the first shutter driving mechanism. FIG. 6B is an illustration fordescribing the state of the second shutter driving mechanism.

As illustrated in FIG. 6A, the D status is a state immediately beforethe first blade 110 starts opening the aperture 105 a. Because the firstmotor Ma is driven counterclockwise in the period from the C status to Dstatus, the first rotor plate 107 is rotated clockwise by the drivingforce of the first motor Ma.

When the first rotor plate 107 rotates clockwise from the stateillustrated in FIG. 5A (C status), the cam pin 109 a in the firstdriving lever 109 follows the first idle running driving region A in thecam groove 107 c in this period. Accordingly, the position of the firstdriving lever 109 in the state illustrated in FIG. 6A (D status) issubstantially the same as the position of the first driving lever 109 inthe state illustrated in FIG. 5A (C status).

As illustrated in FIG. 6B, in D status, the second blade 120 opens theaperture 105 a. In the period from the C status to a state before the Dstatus, because the second motor Mb is driven counterclockwise, thesecond rotor plate 117 is rotated clockwise by a combined force of thedriving force of the second motor Mb and the urging force of the secondspring 118. The urging force of the second spring 118 is provided to thesecond rotor plate 117 up to the state before the D status illustratedin FIG. 6B. That is, in D status illustrated in FIG. 6B, the urgingforce of the second spring 118 is not provided to the second rotor plate117, and the second rotor plate 117 is rotated clockwise by only thedriving force of the second motor Mb.

When the second rotor plate 117 rotates clockwise from the stateillustrated in FIG. 5B (C status), the cam pin 119 a in the seconddriving lever 119 also follows the first idle running driving region Ain the cam groove 117 c in this period. Accordingly, the position of thesecond driving lever 119 in the state illustrated in FIG. 6B (D status)is substantially the same as the position of the second driving lever119 in the state illustrated in FIG. 5B (C status).

As illustrated in FIG. 12, in D status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivencounterclockwise in feed-back driving mode with high advance angle. In Dstatus, the control circuit 13 also controls the driving circuit 14 bsuch that the second motor Mb is driven counterclockwise in step drivingmode. Thus the shutter unit 20 moves to the E status illustrated in FIG.12. The first shutter driving mechanism starts driving for exposure infeed-back driving mode with high advance angle in D status.

FIGS. 7A and 7B are illustrations for describing a state of the shutterunit 20 in E status. FIG. 7A is an illustration for describing the stateof the first shutter driving mechanism. FIG. 7B is an illustration fordescribing the state of the second shutter driving mechanism.

As illustrated in FIG. 7A, in E status, the first blade 110 opens theaperture 105 a. Because the first motor Ma is driven counterclockwise inthe period from the D status to E status, the first rotor plate 107 isrotated clockwise by the driving force of the first motor Ma.

When the first rotor plate 107 rotates clockwise from the stateillustrated in FIG. 6A (D status), the cam pin 109 a in the firstdriving lever 109 follows the exposure driving region B in the camgroove 107 c in this period. This causes the first blade 110 to open theclosed aperture 105 a. Accordingly, in exposure driving, it is necessaryto drive the first motor Ma at high speeds, and this leads to largevariations in load during the driving of the first motor Ma. At thistime, because the first motor Ma is driven in feed-back driving modewith high advance angle, the high-speed driving and the load variationsdo not cause the first motor Ma to lose synchronization. Because therotation speed of the first motor Ma is sufficiently high due to thedriving for the approach run, the first motor Ma can be driven infeed-back driving mode with high advance angle.

As illustrated in FIG. 7B, the E status is a state immediately beforethe second blade 120 starts closing the aperture 105 a. In the periodfrom the D status to E status, because the second motor Mb is drivencounterclockwise, the second rotor plate 117 is rotated clockwise by thedriving force of the second motor Mb.

When the second rotor plate 117 rotates clockwise from the stateillustrated in FIG. 6B (D status), the cam pin 119 a in the seconddriving lever 119 follows the first idle running driving region A in thecam groove 117 c in this period. Accordingly, the position of the seconddriving lever 119 in the state illustrated in FIG. 7B (E status) issubstantially the same as the position of the second driving lever 119in the state illustrated in FIG. 6B (D status).

As illustrated in FIG. 12, in E status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivencounterclockwise in feed-back driving mode with high advance angle. In Estatus, the control circuit 13 also controls the driving circuit 14 bsuch that the second motor Mb is driven counterclockwise in feed-backdriving mode with high advance angle. Thus the shutter unit 20 moves tothe F status illustrated in FIG. 12. The second shutter drivingmechanism starts driving for exposure in feed-back driving mode withhigh advance angle in E status.

FIGS. 8A and 8B are illustrations for describing a state of the shutterunit 20 in F status. FIG. 8A is an illustration for describing the stateof the first shutter driving mechanism. FIG. 8B is an illustration fordescribing the state of the second shutter driving mechanism.

As illustrated in FIG. 8A, in F status, the first blade 110 opens theaperture 105 a. Because the first motor Ma is driven counterclockwise inthe period from the D status to E status, the first rotor plate 107 isrotated clockwise by the driving force of the first motor Ma.

When the first rotor plate 107 rotates clockwise from the stateillustrated in FIG. 7A (E status), the cam pin 109 a in the firstdriving lever 109 follows the second idle running driving region C inthe cam groove 107 c in this period. Accordingly, the position of thefirst driving lever 109 in the state illustrated in FIG. 8A (F status)is substantially the same as the position of the first driving lever 109in the state illustrated in FIG. 7A (E status).

As illustrated in FIG. 8B, in F status, the second blade 120 closes theaperture 105 a. In the period from the E status to F status, because thesecond motor Mb is driven counterclockwise, the second rotor plate 117is rotated clockwise by the driving force of the second motor Mb.

When the second rotor plate 117 rotates clockwise from the stateillustrated in FIG. 7B (E status), the cam pin 119 a in the seconddriving lever 119 follows the exposure driving region B in the camgroove 117 c in this period. This causes the second blade 120 to closethe opened aperture 105 a. Accordingly, in exposure driving, it isnecessary to drive the second motor Mb at high speeds, and this leads tolarge variations in load during the driving of the second motor Mb. Atthis time, because the second motor Mb is driven in feed-back drivingmode with high advance angle, the high-speed driving and the loadvariations do not cause the second motor Mb to lose synchronization.Because the rotation speed of the second motor Mb is sufficiently highdue to the driving for the approach run, the second motor Mb can bedriven in feed-back driving mode with high advance angle.

As illustrated in FIG. 12, in F status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivencounterclockwise in feed-back driving mode with high advance angle. In Fstatus, the control circuit 13 also controls the driving circuit 14 bsuch that the second motor Mb is driven counterclockwise in feed-backdriving mode with high advance angle. Thus the shutter unit 20 moves tothe G status illustrated in FIG. 12.

FIGS. 9A and 9B are illustrations for describing a state of the shutterunit 20 in G status. FIG. 9A is an illustration for describing the stateof the first shutter driving mechanism. FIG. 9B is an illustration fordescribing the state of the second shutter driving mechanism.

As illustrated in FIG. 9A, in G status, the first blade 110 opens theaperture 105 a. The first motor Ma is driven counterclockwise in theperiod from the F status to G status. In the period from the F status toG status, the protruding section 107 a in the first rotor plate 107 isin contact with the right arm section of the first spring 108, and thefirst rotor plate 107 rotates clockwise while charging the first spring108. That is, the first spring 108 acts to apply a break to theclockwise rotation of the first rotor plate 107. In the stateillustrated in FIG. 9A, the first spring 108 is charged, and the firstrotor plate 107 is urged in a counterclockwise direction by the firstspring 108.

When the first rotor plate 107 rotates clockwise from the stateillustrated in FIG. 8A (F status), the cam pin 109 a in the firstdriving lever 109 follows the second idle running driving region C inthe cam groove 107 c in this period. Accordingly, the position of thefirst driving lever 109 in the state illustrated in FIG. 9A (G status)is substantially the same as the position of the first driving lever 109in the state illustrated in FIG. 8A (F status). In this period, thefirst rotor plate 107 rotates clockwise while charging the first spring108, and thus variations in load during the driving of the first motorMa are large. However, because the first motor Ma is driven in feed-backdriving mode with high advance angle, the first motor Ma does not losesynchronization.

As illustrated in FIG. 9B, in G status, the second blade 120 closes theaperture 105 a. In the period from the F status to G status, because thesecond motor Mb is driven counterclockwise, the second rotor plate 117is rotated clockwise by the driving force of the second motor Mb. In thestate illustrated in FIG. 9B, the protruding section 117 a in the secondrotor plate 117 is in contact with the left arm section of the secondspring 118. However, in this state, the second spring 118 is not chargedand is in its natural state.

When the second rotor plate 117 rotates clockwise from the stateillustrated in FIG. 8B (F status), the cam pin 119 a in the seconddriving lever 119 also follows the second idle running driving region Cin the cam groove 117 c in this period. Accordingly, the position of thesecond driving lever 119 in the state illustrated in FIG. 9B (G status)is substantially the same as the position of the second driving lever119 in the state illustrated in FIG. 8B (F status).

As illustrated in FIG. 12, in G status, the control circuit 13 controlsthe driving circuit 14 a such that current supply to the first motor Mais held. Here, holding the current supply indicates maintaining thephase of the current supply to the coil of the first motor Ma in Gstatus. In G status, the control circuit 13 also controls the drivingcircuit 14 b such that the second motor Mb is driven counterclockwise infeed-back driving mode with high advance angle. Thus the shutter unit 20moves to the H status illustrated in FIG. 12.

FIGS. 10A and 10B are illustrations for describing a state of theshutter unit 20 in H status. FIG. 10A is an illustration for describingthe state of the first shutter driving mechanism. FIG. 10B is anillustration for describing the state of the second shutter drivingmechanism.

As illustrated in FIG. 10A, in H status, the first blade 110 opens theaperture 105 a. Because the current supply to the first motor Ma is heldin G status, the first motor Ma and the first rotor plate 107 remain inG status. That is, the state illustrated in FIG. 10A (H status) is thesame as the state illustrated in FIG. 9A (G status).

As illustrated in FIG. 10B, in H status, the second blade 120 closes theaperture 105 a. In the period from the G status to H status, the secondmotor Mb is driven counterclockwise. In the period from the G status toH status, the protruding section 117 a in the second rotor plate 117 isin contact with the left arm section of the second spring 118, and thesecond rotor plate 117 rotates clockwise while charging the secondspring 118. That is, the second spring 118 acts to apply a break to theclockwise rotation of the second rotor plate 117. In the stateillustrated in FIG. 10B, the second spring 118 is charged, and thesecond rotor plate 117 is urged in a counterclockwise direction by thesecond spring 118.

When the second rotor plate 117 rotates clockwise from the stateillustrated in FIG. 9B (G status), the cam pin 119 a in the seconddriving lever 119 follows the second idle running driving region C inthe cam groove 117 c in this period. Accordingly, the position of thesecond driving lever 119 in the state illustrated in FIG. 10B (H status)is substantially the same as the position of the second driving lever119 in the state illustrated in FIG. 9B (G status). In this period, thesecond rotor plate 117 rotates clockwise while charging the secondspring 118, and thus variations in load during the driving of the secondmotor Mb are large. However, because the second motor Mb is driven infeed-back driving mode with high advance angle, the second motor Mb doesnot lose synchronization.

As described above, the shutter unit 20 according to the presentembodiment performs the first-frame shooting operation from the A statusto H status illustrated in FIG. 12. In the first-frame shootingoperation, the first shutter driving mechanism functions as the leadingblade, and the second shutter driving mechanism functions as thetrailing blade. In the second-frame shooting operation, the secondshutter driving mechanism functions as the leading blade, and the firstshutter driving mechanism functions as the trailing blade. That is, inthe first-frame shooting operation, the first shutter driving mechanismperforms an exposure operation ahead of the second shutter drivingmechanism. In the second-frame shooting operation, the second shutterdriving mechanism performs an exposure operation ahead of the firstshutter driving mechanism.

In the present embodiment, the start of driving for an approach run inthe first shutter driving mechanism is caused to lag behind the start ofdriving for an approach run in the second shutter driving mechanism byan exposure time t2 for the second frame by adjustment of the period oftime for which the current supply to the first motor Ma is held.

As illustrated in FIG. 12, in H status, the control circuit 13 controlsthe driving circuit 14 a such that the current supply to the first motorMa is held. In H status, the control circuit 13 also controls thedriving circuit 14 b such that the second motor Mb is driven clockwisein step driving mode. Thus the second rotor plate 117 is rotatedcounterclockwise by the driving force of the second motor Mb and theurging force of the second spring 118. The second shutter drivingmechanism starts driving for an approach run in step driving mode in Hstatus. Thus the shutter unit 20 moves to the G′ status illustrated inFIG. 12.

The state of the shutter unit 20 in G′ status illustrated in FIG. 12 isthe same as the state illustrated in FIGS. 9A and 9B.

As illustrated in FIG. 12, in G′ status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivenclockwise in step driving mode. Thus the first rotor plate 107 isrotated counterclockwise by the driving force of the first motor Ma andthe urging force of the first spring 108. The first shutter drivingmechanism starts driving for an approach run in step driving mode in G′status. In G′ status, the control circuit 13 controls the drivingcircuit 14 b such that the second motor Mb is driven clockwise in stepdriving mode. Thus the shutter unit 20 moves to the F′ statusillustrated in FIG. 12.

The state of the shutter unit 20 in F′ status illustrated in FIG. 12 isthe same as the state illustrated in FIGS. 8A and 8B.

As illustrated in FIG. 12, in F′ status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivenclockwise in step driving mode. In F′ status, the control circuit 13controls the driving circuit 14 b such that the second motor Mb isdriven clockwise in feed-back driving mode with high advance angle. Thusthe shutter unit 20 moves to the E′ status illustrated in FIG. 12. Thesecond shutter driving mechanism starts driving for exposure infeed-back driving mode with high advance angle in F′ status. Because therotation speed of the second motor Mb is sufficiently high due to thedriving for the approach run, the second motor Mb can be driven infeed-back driving mode with high advance angle.

The state of the shutter unit 20 in F′ status illustrated in FIG. 12 isthe same as the state illustrated in FIG. 8.

As illustrated in FIG. 12, in E′ status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivenclockwise in feed-back driving mode with high advance angle. In E′status, the control circuit 13 controls the driving circuit 14 b suchthat the second motor Mb is driven clockwise in feed-back driving modewith high advance angle. Thus the shutter unit 20 moves to the D′ statusillustrated in FIG. 12. The first shutter driving mechanism startsdriving for exposure in feed-back driving mode with high advance anglein E′ status. Because the rotation speed of the first motor Ma issufficiently high due to the driving for the approach run, the firstmotor Ma can be driven in feed-back driving mode with high advanceangle.

The state of the shutter unit 20 in E′ status illustrated in FIG. 12 isthe same as the state illustrated in FIGS. 7A and 7B.

As illustrated in FIG. 12, in D′ status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivenclockwise in feed-back driving mode with high advance angle. In D′status, the control circuit 13 controls the driving circuit 14 b suchthat the second motor Mb is driven clockwise in feed-back driving modewith high advance angle. Thus the shutter unit 20 moves to the C′ statusillustrated in FIG. 12.

The state of the shutter unit 20 in C′ status illustrated in FIG. 12 isthe same as the state illustrated in FIGS. 6A and 6B.

As illustrated in FIG. 12, in C′ status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivenclockwise in feed-back driving mode with high advance angle. In C′status, the control circuit 13 controls the driving circuit 14 b suchthat the current supply to the second motor Mb is held. Here, holdingthe current supply indicates maintaining the phase of the current supplyto the second motor Mb in D status. Thus the shutter unit 20 moves tothe I status illustrated in FIG. 12.

FIGS. 11A and 11B are illustrations for describing a state of theshutter unit 20 in I status. FIG. 11A is an illustration for describingthe state of the first shutter driving mechanism. FIG. 11B is anillustration for describing the state of the second shutter drivingmechanism.

As illustrated in FIG. 11A, in I status, the first blade 110 closes theaperture 105 a. As illustrated in FIG. 12, because the first motor Ma isdriven clockwise in the period from the C′ status to I status, the firstrotor plate 107 is rotated counterclockwise from the state illustratedin FIG. 5A. In the period from the C′ status to I status, the protrudingsection 107 a in the first rotor plate 107 is in contact with the leftarm section of the first spring 108, and the first rotor plate 107rotates counterclockwise while charging the first spring 108. That is,the first spring 108 acts to apply a break to the counterclockwiserotation of the first rotor plate 107. In the state illustrated in FIG.11A, the first spring 108 is charged, and the first rotor plate 107 isurged in a clockwise direction by the first spring 108.

As illustrated in FIG. 11B, in I status, the second blade 120 opens theaperture 105 a. Because the current supply to the second motor Mb isheld in C′ status, the second motor Mb and the second rotor plate 117remain in C′ status. That is, the state illustrated in FIG. 5B is thesame as the state illustrated in FIG. 11B.

As described above, the shutter unit 20 according to the presentembodiment performs the second-frame shooting operation from the Hstatus to I status illustrated in FIG. 12. In the second-frame shootingoperation, the second shutter driving mechanism functions as the leadingblade, and the first shutter driving mechanism functions as the trailingblade. In the third-frame shooting operation, the first shutter drivingmechanism functions as the leading blade, and the second shutter drivingmechanism functions as the trailing blade. In the present embodiment,the start of driving for an approach run in the second shutter drivingmechanism is caused to lag behind the start of driving for an approachrun in the first shutter driving mechanism by an exposure time t3 forthe third frame by adjustment of the period of time for which thecurrent supply to the second motor Mb is held.

As illustrated in FIG. 12, in I status, the control circuit 13 controlsthe driving circuit 14 a such that the first motor Ma is drivencounterclockwise in step driving mode. The control circuit 13 controlsthe driving circuit 14 b such that the current supply to the secondmotor Mb is held. Thus the shutter unit 20 moves to the C statusillustrated in FIG. 12.

After that, the same shooting operation as that for the first frame isperformed.

(Variation)

FIG. 13 is a timing chart for describing operations of the shutter unit20 when the camera 100 is operating in continuous shooting mode as avariation of the present embodiment.

In the above-described embodiment, a lag between the leading blade andthe trailing blade is produced by making the timing for starting thedriving for the approach run in the shutter driving mechanismfunctioning as the leading blade and the timing for starting the drivingfor the approach run in the shutter driving mechanism functioning as thetrailing blade different.

In contrast, in the variation, a lag between the leading blade and thetrailing blade is produced by making a pulse rate for the driving forthe approach run in the shutter driving mechanism functioning as theleading blade and a pulse rate for the driving for the approach run inthe shutter driving mechanism functioning as the trailing bladedifferent. That is, the pulse rate for the driving for the approach runin the shutter driving mechanism functioning as the leading blade is setat a value larger than the pulse rate for the driving for the approachrun in the shutter driving mechanism functioning as the trailing blade.Thus even in the same approach run period, the time required for thedriving for the approach run in the shutter driving mechanismfunctioning as the trailing blade is longer than the time required forthe driving for the approach run in the shutter driving mechanismfunctioning as the leading blade.

In the variation, in A status illustrated in FIG. 13, the controlcircuit 13 controls the driving circuit 14 a such that the first motorMa is driven clockwise in feed-back driving mode with low advance angle.In A status illustrated in FIG. 13, the control circuit 13 controls thedriving circuit 14 b such that the second motor Mb is driven clockwisein feed-back driving mode with low advance angle. Thus the shutter unit20 moves to the I status illustrated in FIG. 13.

In I status illustrated in FIG. 13, the control circuit 13 controls thedriving circuit 14 a such that the first motor Ma is drivencounterclockwise in step driving mode. In I status illustrated in FIG.13, the control circuit 13 controls the driving circuit 14 b such thatthe second motor Mb is driven counterclockwise in step driving mode.Thus the shutter unit 20 moves to the D status illustrated in FIG. 13.

The state from the D status to G status illustrated in FIG. 13 is thesame as that from the D status to G status illustrated in FIG. 12 in theembodiment described above.

In G status illustrated in FIG. 13, the control circuit 13 also controlsthe driving circuit 14 a such that the first motor Ma is drivencounterclockwise in feed-back driving mode with high advance angle. In Dstatus illustrated in FIG. 13, the control circuit 13 also controls thedriving circuit 14 b such that the second motor Mb is drivencounterclockwise in feed-back driving mode with high advance angle.

In the above-described embodiment, in G status illustrated in FIG. 12,the control circuit 13 controls the driving circuit 14 a such that thecurrent supply to the first motor Ma is held. In the variation, thecontrol circuit 13 controls the driving circuit 14 a such that the firstmotor Ma is driven counterclockwise in feed-back driving mode with highadvance angle. Accordingly, although the first rotor plate 107 tries torotate clockwise, because the protruding section 107 a in the firstrotor plate 107 comes into contact with the stopper on the cover plate103, the clockwise rotation of the first rotor plate 107 is blocked.

The characteristics in the variation are substantially the same as thosein the above-described embodiment, except for the method of producing alag between the leading blade and the trailing blade and the respect inwhich holding the current supply is not performed.

Next, the details of the first motor Ma and the second motor Mb aredescribed with reference to FIGS. 14 to 16.

FIG. 14 illustrates a motor 1 used as each of the first motor Ma and thesecond motor Mb. For the sake of the description, parts of somecomponents are removed in the illustration.

As illustrated in FIG. 14, a rotor 3 includes a magnet 2 and isrotatably controlled by the control circuit (controller) 13 and thedriving circuit 14. The magnet 2 is cylindrical, has a circumferentialsurface divided in its circumferential direction, and ismultipole-magnetized in different poles in an alternatingly manner. Inthe present embodiment, the magnet 2 is divided in eight elements, thatis, magnetized in eight poles. The number of divisions is not limited toeight. The magnet 2 may be magnetized in four or twelve poles.

A first coil 4 is arranged on a first end of the magnet 2 in its axialdirection.

A first yoke 6 is made of a soft magnetic material and is opposed to thecircumferential surface of the magnet 2 such that a gap is presenttherebetween. The first yoke 6 axially extends from an annular main bodyportion and includes a plurality of first magnetic pole sections 6 aarranged at predetermined intervals in its circumferential direction.The first magnetic pole sections 6 a are excited by energization of thefirst coil 4.

The first coil 4, the first yoke 6, and the magnet 2 opposed to theplurality of first magnetic pole sections 6 a constitute a first statorunit.

A second coil 5 is arranged on a second end of the magnet 2 in its axialdirection, and the second end is opposite to the first end on which thefirst coil 4 is arranged.

A second yoke 7 is made of a soft magnetic material and is opposed tothe circumferential surface of the magnet 2 such that a gap is presenttherebetween. The second yoke 7 axially extends from the annular mainbody portion and includes a plurality of second magnetic pole sections 7a arranged at predetermined intervals in its circumferential direction.The second magnetic pole sections 7 a are excited by energization of thesecond coil 5.

The second coil 5, the second yoke 7, and the magnet 2 opposed to theplurality of second magnetic pole sections 7 a constitute a secondstator unit.

A torque provided to the rotor 3 can be changed by switching themagnetized polarity (north pole, south pole) of each of the firstmagnetic pole sections 6 a and the second magnetic pole sections 7 a.

A first magnetic sensor (first detecting element) 8, a second magneticsensor (second detecting element) 9, a third magnetic sensor (thirddetecting element) 10, and a fourth magnetic sensor (fourth detectingelement) 11 constitute detecting means. Each of the magnetic sensors isa Hall element configured to detect a magnetic flux of the magnet 2 andis fixed to a motor cover 12.

The motor cover 12 fixes and retains the first yoke 6 and the secondyoke 7 such that the first magnetic pole sections 6 a and the secondmagnetic pole sections 7 a are displaced with respect to a magnetizationphase of the magnet 2 by approximately 90 degrees in electrical angle.

Here, the electrical angle is an angle represented based on theassumption that one cycle of the magnetic force of the magnet is 360°.The electrical angle θ can be expressed by the following equation:

θ=θ0×M/2

where M is the number of poles of the rotor, and the mechanical angle isθ0.

In the present embodiment, the magnet 2 is magnetized in eight poles,and 90 degrees in electrical angle is 22.5 degrees in mechanical angle.

The control circuit 13 can switch the driving among the step driving andthe two kinds of feed-back driving with different amounts of the advanceangle. In step driving, the control circuit 13 controls the drivingcircuit 14 such that the energization state of the first coil 4 and thesecond coil 5 is switched at predetermined time intervals. That is, instep driving, none of outputs of the first magnetic sensor 8, the secondmagnetic sensor 9, the third magnetic sensor 10, and the fourth magneticsensor 11 are used.

A case where the control circuit 13 performs the feed-back driving isdescribed below. When the control circuit 13 performs the two kinds offeed-back driving, outputs of the first magnetic sensor 8, the secondmagnetic sensor 9, the third magnetic sensor 10, and the fourth magneticsensor 11 are used.

In the present embodiment, even in switching the energization direction,a large rotational driving force is obtainable by arranging eachmagnetic sensor in a positional relationship with respect to each yokedescribed below.

FIGS. 15A to 151 are illustrations for describing operations of themotor 1. Actual operations of the motor 1 are described with referenceto FIGS. 15A to 151. The state in FIG. 15A is described as an initialstate in driving.

(1) Clockwise Driving

(1-i) Low Advance Angle Driving (First Energization Mode)

The clockwise driving mode with low advance angle is described. Thedriving mode with low advance angle can achieve larger torque than thatin the driving mode with high advance angle described below.

In the clockwise driving mode with low advance angle, the rotor 3 isrotated clockwise by switching excitation of each of the first magneticpole sections 6 a in response to an output signal of the first magneticsensor 8 and switching excitation of each of the second magnetic polesections 7 a in response to an output signal of the second magneticsensor 9. The direction of the clockwise rotation of the rotor 3corresponds to a first rotation direction.

In this driving mode, the energization direction of each of the firstcoil 4 and the second coil 5 is switched using combinations describedbelow.

When the first magnetic sensor 8 detects the south pole of the magnet 2(switching from the north pole to south pole), its detection signal isinput into the control circuit 13. The control circuit 13 controls thedriving circuit 14 such that the first magnetic pole section 6 a ismagnetized with the north pole. When the first magnetic sensor 8 detectsthe north pole of the magnet 2 (switching from the south pole to northpole), its detection signal is input into the control circuit 13. Thecontrol circuit 13 controls the driving circuit 14 such that the firstmagnetic pole section 6 a is magnetized with the south pole.

When the second magnetic sensor 9 detects the south pole of the magnet 2(switching from the north pole to south pole), its detection signal isinput into the control circuit 13. The control circuit 13 controls thedriving circuit 14 such that the second magnetic pole section 7 a ismagnetized with the south pole. When the second magnetic sensor 9detects the north pole of the magnet 2 (switching from the south pole tonorth pole), its detection signal is input into the control circuit 13.The control circuit 13 controls the driving circuit 14 such that thesecond magnetic pole section 7 a is magnetized with the north pole.

In the state illustrated in FIG. 15A, both the first magnetic sensor 8and the second magnetic sensor 9 detect the south pole of the magnet 2.At this time, the control circuit 13 controls the driving circuit 14such that the first magnetic pole section 6 a is magnetized with thenorth pole and the second magnetic pole section 7 a is magnetized withthe south pole. This produces a clockwise rotation force in the rotor 3and the magnet 2.

When the rotor 3 rotates clockwise from the state illustrated in FIG.15A, the center Q1 of each of the south poles of the magnet 2 and thecenter of the corresponding first magnetic pole section 6 a are opposedto each other, as illustrated in FIG. 15B.

When the rotor 3 rotates clockwise from the state illustrated in FIG.15B, the distance between the center Q1 of the south pole of the magnet2 and the first magnetic pole section 6 a is the same as the distancebetween the center Q2 of each of the north poles of the magnet 2 and thecorresponding second magnetic pole section 7 a, as illustrated in FIG.15C.

The first magnetic sensor 8 is arranged such that when the magnetizedpolarity of the first magnetic pole section 6 a is switched on the basisof the output of the first magnetic sensor 8, the excitation switchingtiming for the first magnetic pole section 6 a with respect to therotation position of the rotor 3 corresponds to an electrical advanceangle between angle 0 degree to 45 degrees.

The first magnetic sensor 8 detects the north pole of the magnet 2(switching from the south pole to north pole) between the stateillustrated in FIG. 15B and the state illustrated in FIG. 15C. At thistime, the driving circuit 14 energizes the first coil 4 such that thefirst magnetic pole section 6 a is magnetized with the south pole.Because the second magnetic sensor 9 detects the south pole of themagnet 2 between the state illustrated in FIG. 15B and the stateillustrated in FIG. 15C, the driving circuit 14 energizes the secondcoil 5 such that the second magnetic pole section 7 a is magnetized withthe south pole. This produces the clockwise rotation force in the rotor3 and the magnet 2.

When the rotor 3 rotates clockwise from the state illustrated in FIG.15C, the center Q2 of the north pole of the magnet 2 and the center ofthe second magnetic pole section 7 a are opposed to each other, asillustrated in FIG. 15D.

When the rotor 3 rotates clockwise from the state illustrated in FIG.15D, the distance between the center Q2 of the north pole of the magnet2 and the first magnetic pole section 6 a is the same as the distancebetween the center Q2 of the north pole of the magnet 2 and the secondmagnetic pole section 7 a, as illustrated in FIG. 15E.

The second magnetic sensor 9 is arranged such that when the magnetizedpolarity of the second magnetic pole section 7 a is switched on thebasis of the output of the second magnetic sensor 9, the excitationswitching timing for the second magnetic pole section 7 a with respectto the rotation position of the rotor 3 corresponds to an electricaladvance angle between 0 degree to 45 degrees.

The second magnetic sensor 9 detects the north pole of the magnet 2(switching from the south pole to north pole) between the stateillustrated in FIG. 15D and the state illustrated in FIG. 15E. At thistime, the driving circuit 14 energizes the second coil 5 such that thesecond magnetic pole section 7 a is magnetized with the north pole.Because the first magnetic sensor 8 detects the north pole of the magnet2 between the state illustrated in FIG. 15D and the state illustrated inFIG. 15E, the driving circuit 14 energizes the first coil 4 such thatthe first magnetic pole section 6 a is magnetized with the south pole.This produces the clockwise rotation force in the rotor 3 and the magnet2.

As described above, in the clockwise driving mode with low advanceangle, the energization of the first coil 4 and the second coil 5 issequentially switched by the outputs of the first magnetic sensor 8 andthe second magnetic sensor 9, and the rotor 3 and the magnet 2 rotate ina clockwise direction.

When the rotor 3 rotates clockwise and the magnetized polarity of thefirst magnetic pole section 6 a is switched on the basis of the outputof the first magnetic sensor 8, the excitation switching timing for thefirst magnetic pole section 6 a with respect to the rotation position ofthe rotor 3 corresponds to an electrical advance angle between angle 0degree to 45 degrees. That is, the first magnetic sensor 8 is arrangedin a position where the amount of the advance angle from the position ofthe electrical advance angle 0 degree from the excitation switchingtiming at the first magnetic pole section 6 a is smaller than the amountof the lag angle from the position of the electrical advance angle 90degrees from the excitation switching timing at the first magnetic polesection 6 a.

When the rotor 3 rotates clockwise and the magnetized polarity of thesecond magnetic pole section 7 a is switched on the basis of the outputof the second magnetic sensor 9, the excitation switching timing for thesecond magnetic pole section 7 a with respect to the rotation positionof the rotor 3 corresponds to an electrical advance angle between angle0 degree to 45 degrees. That is, the second magnetic sensor 9 isarranged in a position where the amount of the advance angle from theposition of the electrical advance angle 0 degree from the excitationswitching timing at the second magnetic pole section 7 a is smaller thanthe amount of the lag angle from the position of the electrical advanceangle 90 degrees from the excitation switching timing at the secondmagnetic pole section 7 a.

(1-ii) High Advance Angle Driving (Second Energization Mode)

The clockwise driving mode with high advance angle is described. Thedriving mode with high advance angle can achieve higher speed rotationthan that in the above-described driving mode with low advance angle.

In the clockwise driving mode with high advance angle, the rotor 3 isrotated clockwise by switching the magnetized polarity of the firstmagnetic pole section 6 a in response to the output of the thirdmagnetic sensor 10 and switching the magnetized polarity of the secondmagnetic pole section 7 a in response to the output of the fourthmagnetic sensor 11.

In this driving mode, the energization direction of each of the firstcoil 4 and the second coil 5 is switched using combinations describedbelow.

When the third magnetic sensor 10 detects the south pole of the magnet 2(switching from the north pole to south pole), its detection signal isinput into the control circuit 13. The control circuit 13 controls thedriving circuit 14 such that the first magnetic pole section 6 a ismagnetized with the north pole. When the third magnetic sensor 10detects the north pole of the magnet 2 (switching from the south pole tonorth pole), its detection signal is input into the control circuit 13.The control circuit 13 controls the driving circuit 14 such that thefirst magnetic pole section 6 a is magnetized with the south pole.

When the fourth magnetic sensor 11 detects the south pole of the magnet2 (switching from the north pole to south pole), its detection signal isinput into the control circuit 13. The control circuit 13 controls thedriving circuit 14 such that the second magnetic pole section 7 a ismagnetized with the south pole. When the fourth magnetic sensor 11detects the north pole of the magnet 2 (switching from the south pole tonorth pole), its detection signal is input into the control circuit 13.The control circuit 13 controls the driving circuit 14 such that thesecond magnetic pole section 7 a is magnetized with the north pole.

In the state illustrated in FIG. 15A, both the third magnetic sensor 10and the fourth magnetic sensor 11 detect the south pole of the magnet 2.Accordingly, when the first magnetic pole section 6 a is magnetized withthe north pole and the second magnetic pole section 7 a is magnetizedwith the south pole, a clockwise rotation force is produced in the rotor3 and the magnet 2.

When the rotor 3 rotates clockwise from the state illustrated in FIG.15A, the center Q1 of each of the south poles of the magnet 2 and thecenter of the corresponding first magnetic pole section 6 a are opposedto each other, as illustrated in FIG. 15B.

The third magnetic sensor 10 is arranged such that when the magnetizedpolarity of the first magnetic pole section 6 a is switched on the basisof the output of the third magnetic sensor 10, the excitation switchingtiming for the first magnetic pole section 6 a with respect to therotation position of the rotor 3 corresponds to an electrical advanceangle between angle 45 degrees to 90 degrees.

The third magnetic sensor 10 detects the north pole of the magnet 2(switching from the south pole to north pole) between the stateillustrated in FIG. 15A and the state illustrated in FIG. 15B. At thistime, the driving circuit 14 energizes the first coil 4 such that thefirst magnetic pole section 6 a is magnetized with the south pole.Because the fourth magnetic sensor 11 detects the south pole of themagnet 2 between the state illustrated in FIG. 15A and the stateillustrated in FIG. 15B, the driving circuit 14 energizes the secondcoil 5 such that the second magnetic pole section 7 a is magnetized withthe south pole. This produces the clockwise rotation force in the rotor3 and the magnet 2.

When the rotor 3 rotates clockwise from the state illustrated in FIG.15B, the state moves to the state illustrated in FIG. 15C, and then thecenter Q2 of the north pole of the magnet 2 and the center of the secondmagnetic pole section 7 a are opposed to each other, as illustrated inFIG. 15D.

The fourth magnetic sensor 11 is arranged such that when the magnetizedpolarity of the second magnetic pole section 7 a is switched on thebasis of the output of the fourth magnetic sensor 11, the excitationswitching timing for the second magnetic pole section 7 a with respectto the rotation position of the rotor 3 corresponds to an electricaladvance angle between 45 degrees to 90 degrees.

The fourth magnetic sensor 11 detects the north pole of the magnet 2(switching from the south pole to north pole) between the stateillustrated in FIG. 15C and the state illustrated in FIG. 15D. At thistime, the driving circuit 14 energizes the second coil 5 such that thesecond magnetic pole section 7 a is magnetized with the north pole.Because the third magnetic sensor 10 detects the north pole of themagnet 2 between the state illustrated in FIG. 15C and the stateillustrated in FIG. 15D, the driving circuit 14 energizes the first coil4 such that the first magnetic pole section 6 a is magnetized with thesouth pole. This produces the clockwise rotation force in the rotor 3and the magnet 2.

As described above, in the clockwise driving mode with high advanceangle, the energization of the first coil 4 and the second coil 5 issequentially switched by the outputs of the third magnetic sensor 10 andthe fourth magnetic sensor 11, and the rotor 3 and the magnet 2 rotatein a clockwise direction.

When the rotor 3 rotates clockwise and the magnetized polarity of thefirst magnetic pole section 6 a is switched on the basis of the outputof the third magnetic sensor 10, the excitation switching timing for thefirst magnetic pole section 6 a with respect to the rotation position ofthe rotor 3 corresponds to an electrical advance angle between angle 45degrees to 90 degrees. That is, the third magnetic sensor 10 is arrangedin a position where the amount of the advance angle from the position ofthe electrical advance angle 0 degree from the excitation switchingtiming at the first magnetic pole section 6 a is larger than the amountof the lag angle from the position of the electrical advance angle 90degrees from the excitation switching timing at the first magnetic polesection 6 a.

When the rotor 3 rotates clockwise and the magnetized polarity of thesecond magnetic pole section 7 a is switched on the basis of the outputof the fourth magnetic sensor 11, the excitation switching timing forthe second magnetic pole section 7 a with respect to the rotationposition of the rotor 3 corresponds to an electrical advance anglebetween angle 45 degrees to 90 degrees. That is, the fourth magneticsensor 11 is arranged in a position where the amount of the advanceangle from the position of the electrical advance angle 0 degree fromthe excitation switching timing at the second magnetic pole section 7 ais larger than the amount of the lag angle from the position of theelectrical advance angle 90 degrees from the excitation switching timingat the second magnetic pole section 7 a.

(2) Counterclockwise Driving

(2-i) Low Advance Angle Driving (Third Energization Mode)

The counterclockwise driving mode with low advance angle is described.Even for the counterclockwise rotation, the driving mode with lowadvance angle can achieve larger torque than that in the driving modewith high advance angle.

In the counterclockwise driving mode with low advance angle, the rotor 3is rotated counterclockwise by switching excitation of each of the firstmagnetic pole sections 6 a in response to an output signal of the thirdmagnetic sensor 10 and switching excitation of each of the secondmagnetic pole sections 7 a in response to an output signal of the fourthmagnetic sensor 11. The direction of the counterclockwise rotation ofthe rotor 3 corresponds to a second rotation direction opposite to thefirst rotation direction.

In this driving mode, the energization direction of each of the firstcoil 4 and the second coil 5 is switched using combinations describedbelow.

When the third magnetic sensor 10 detects the south pole of the magnet 2(switching from the north pole to south pole), its detection signal isinput into the control circuit 13. The control circuit 13 controls thedriving circuit 14 such that the first magnetic pole section 6 a ismagnetized with the south pole. When the third magnetic sensor 10detects the north pole of the magnet 2 (switching from the south pole tonorth pole), its detection signal is input into the control circuit 13.The control circuit 13 controls the driving circuit 14 such that thefirst magnetic pole section 6 a is magnetized with the north pole.

When the fourth magnetic sensor 11 detects the south pole of the magnet2 (switching from the north pole to south pole), its detection signal isinput into the control circuit 13. The control circuit 13 controls thedriving circuit 14 such that the second magnetic pole section 7 a ismagnetized with the north pole. When the fourth magnetic sensor 11detects the north pole of the magnet 2 (switching from the south pole tonorth pole), its detection signal is input into the control circuit 13.The control circuit 13 controls the driving circuit 14 such that thesecond magnetic pole section 7 a is magnetized with the south pole.

In the state illustrated in FIG. 15A, both the third magnetic sensor 10and the fourth magnetic sensor 11 detect the south pole of the magnet 2.At this time, the control circuit 13 controls the driving circuit 14such that the first magnetic pole section 6 a is magnetized with thesouth pole and the second magnetic pole section 7 a is magnetized withthe north pole. This produces a counterclockwise rotation force in therotor 3 and the magnet 2.

When the rotor 3 rotates counterclockwise from the state illustrated inFIG. 15A, the center Q1 of the south pole of the magnet 2 and the centerof the second magnetic pole section 7 a are opposed to each other, asillustrated in FIG. 15F.

When the rotor 3 rotates counterclockwise from the state illustrated inFIG. 15F, the distance between the center Q1 of the south pole of themagnet 2 and the second magnetic pole section 7 a is the same as thedistance between the center Q3 of the north pole of the magnet 2 and thefirst magnetic pole section 6 a, as illustrated in FIG. 15G.

The fourth magnetic sensor 11 is arranged such that when the magnetizedpolarity of the second magnetic pole section 7 a is switched on thebasis of the output of the fourth magnetic sensor 11, the excitationswitching timing for the second magnetic pole section 7 a with respectto the rotation position of the rotor 3 corresponds to an electricaladvance angle between 0 degree to 45 degrees.

The north pole of the magnet 2 (switching from the south pole to northpole) is detected between the state illustrated in FIG. 15F and thestate illustrated in FIG. 15G. At this time, the driving circuit 14energizes the second coil 5 such that the second magnetic pole section 7a is magnetized with the south pole. Because the third magnetic sensor10 detects the south pole of the magnet 2 between the state illustratedin FIG. 15F and the state illustrated in FIG. 15G, the driving circuit14 energizes the first coil 4 such that the first magnetic pole section6 a is magnetized with the south pole. This produces thecounterclockwise rotation force in the rotor 3 and the magnet 2.

When the rotor 3 rotates counterclockwise from the state illustrated inFIG. 15G, the center Q3 of the north pole of the magnet 2 and the centerof the first magnetic pole section 6 a are opposed to each other, asillustrated in FIG. 15H.

When the rotor 3 rotates counterclockwise from the state illustrated inFIG. 15H, the distance between the center Q3 of the north pole of themagnet 2 and the first magnetic pole section 6 a is the same as thedistance between the center Q3 of the north pole of the magnet 2 and thesecond magnetic pole section 7 a, as illustrated in FIG. 15I.

The third magnetic sensor 10 is arranged such that when the magnetizedpolarity of the first magnetic pole section 6 a is switched on the basisof the output of the third magnetic sensor 10, the excitation switchingtiming for the first magnetic pole section 6 a with respect to therotation position of the rotor 3 corresponds to an electrical advanceangle between angle 0 degree to 45 degrees.

The third magnetic sensor 10 detects the north pole of the magnet 2(switching from the south pole to north pole) between the stateillustrated in FIG. 15H and the state illustrated in FIG. 15I. At thistime, the driving circuit 14 energizes the first coil 4 such that thefirst magnetic pole section 6 a is magnetized with the north pole.Because the fourth magnetic sensor 11 detects the north pole of themagnet 2 between the state illustrated in FIG. 15H and the stateillustrated in FIG. 15I, the driving circuit 14 energizes the secondcoil 5 such that the second magnetic pole section 7 a is magnetized withthe south pole. This produces the counterclockwise rotation force in therotor 3 and the magnet 2.

As described above, in the counterclockwise driving mode with lowadvance angle, the energization of the first coil 4 and the second coil5 is sequentially switched by the outputs of the third magnetic sensor10 and the fourth magnetic sensor 11, and the rotor 3 and the magnet 2rotate in a counterclockwise direction.

When the rotor 3 rotates counterclockwise and the magnetized polarity ofthe first magnetic pole section 6 a is switched on the basis of theoutput of the third magnetic sensor 10, the excitation switching timingfor the first magnetic pole section 6 a with respect to the rotationposition of the rotor 3 corresponds to an electrical advance anglebetween angle 0 degree to 45 degrees.

When the rotor 3 rotates counterclockwise and the magnetized polarity ofthe second magnetic pole section 7 a is switched on the basis of theoutput of the fourth magnetic sensor 11, the excitation switching timingfor the second magnetic pole section 7 a with respect to the rotationposition of the rotor 3 corresponds to an electrical advance anglebetween angle 0 degree to 45 degrees.

(2-ii) High Advance Angle Driving (Fourth Energization Mode)

The counterclockwise driving mode with high advance angle is described.Even for the counterclockwise rotation, the driving mode with highadvance angle can achieve higher speed rotation than that in theabove-described driving mode with low advance angle.

In the counterclockwise driving mode with high advance angle, the rotor3 is rotated counterclockwise by switching excitation of each of thefirst magnetic pole sections 6 a in response to an output signal of thefirst magnetic sensor 8 and switching excitation of each of the secondmagnetic pole sections 7 a in response to an output signal of the secondmagnetic sensor 9.

In this driving mode, the energization direction of each of the firstcoil 4 and the second coil 5 is switched using combinations describedbelow.

When the first magnetic sensor 8 detects the south pole of the magnet 2(switching from the north pole to south pole), its detection signal isinput into the control circuit 13. The control circuit 13 controls thedriving circuit 14 such that the first magnetic pole section 6 a ismagnetized with the south pole. When the first magnetic sensor 8 detectsthe north pole of the magnet 2 (switching from the south pole to northpole), its detection signal is input into the control circuit 13. Thecontrol circuit 13 controls the driving circuit 14 such that the firstmagnetic pole section 6 a is magnetized with the north pole.

When the second magnetic sensor 9 detects the south pole of the magnet 2(switching from the north pole to south pole), its detection signal isinput into the control circuit 13. The control circuit 13 controls thedriving circuit 14 such that the second magnetic pole section 7 a ismagnetized with the north pole. When the second magnetic sensor 9detects the north pole of the magnet 2 (switching from the south pole tonorth pole), its detection signal is input into the control circuit 13.The control circuit 13 controls the driving circuit 14 such that thesecond magnetic pole section 7 a is magnetized with the south pole.

In the state illustrated in FIG. 15A, both the first magnetic sensor 8and the second magnetic sensor 9 detect the south pole of the magnet 2.Accordingly, when the first magnetic pole section 6 a is magnetized withthe south pole and the second magnetic pole section 7 a is magnetizedwith the north pole, the counterclockwise rotation force is produced inthe rotor 3 and the magnet 2.

When the rotor 3 rotates counterclockwise from the state illustrated inFIG. 15A, the center Q1 of the south pole of the magnet 2 and the centerof the second magnetic pole section 7 a are opposed to each other, asillustrated in FIG. 15F.

The second magnetic sensor 9 is arranged such that when the magnetizedpolarity of the second magnetic pole section 7 a is switched on thebasis of the output of the second magnetic sensor 9, the excitationswitching timing for the second magnetic pole section 7 a with respectto the rotation position of the rotor 3 corresponds to an electricaladvance angle between 45 degrees to 90 degrees.

The second magnetic sensor 9 detects the north pole of the magnet 2(switching from the south pole to north pole) between the stateillustrated in FIG. 15A and the state illustrated in FIG. 15F. At thistime, the driving circuit 14 energizes the second coil 5 such that thesecond magnetic pole section 7 a is magnetized with the north pole.Because the first magnetic sensor 8 detects the south pole of the magnet2 between the state illustrated in FIG. 15A and the state illustrated inFIG. 15F, the driving circuit 14 energizes the first coil 4 such thatthe first magnetic pole section 6 a is magnetized with the south pole.This produces the counterclockwise rotation force in the rotor 3 and themagnet 2.

When the rotor 3 rotates counterclockwise from the state illustrated inFIG. 15F, the state moves to the state illustrated in FIG. 15G, and thenthe center Q3 of the north pole of the magnet 2 and the center of thefirst magnetic pole section 6 a are opposed to each other, asillustrated in FIG. 15H.

The first magnetic sensor 8 is arranged such that when the magnetizedpolarity of the first magnetic pole section 6 a is switched on the basisof the output of the first magnetic sensor 8, the excitation switchingtiming for the first magnetic pole section 6 a with respect to therotation position of the rotor 3 corresponds to an electrical advanceangle between 45 degrees to 90 degrees.

The first magnetic sensor 8 detects the north pole of the magnet 2(switching from the south pole to north pole) between the stateillustrated in FIG. 15G and the state illustrated in FIG. 15H. At thistime, the driving circuit 14 energizes the first coil 4 such that thefirst magnetic pole section 6 a is magnetized with the north pole.Because the second magnetic sensor 9 detects the north pole of themagnet 2 between the state illustrated in FIG. 15G and the stateillustrated in FIG. 15H, the driving circuit 14 energizes the secondcoil 5 such that the second magnetic pole section 7 a is magnetized withthe south pole. This produces the counterclockwise rotation force in therotor 3 and the magnet 2.

As described above, in the counterclockwise driving mode with highadvance angle, the energization of the first coil 4 and the second coil5 is sequentially switched by the outputs of the first magnetic sensor 8and the second magnetic sensor 9, and the rotor 3 and the magnet 2rotate in a counterclockwise direction.

When the rotor 3 rotates counterclockwise and the magnetized polarity ofthe first magnetic pole section 6 a is switched on the basis of theoutput of the first magnetic sensor 8, the excitation switching timingfor the first magnetic pole section 6 a with respect to the rotationposition of the rotor 3 corresponds to an electrical advance anglebetween angle 45 degrees to 90 degrees.

When the rotor 3 rotates counterclockwise and the magnetized polarity ofthe second magnetic pole section 7 a is switched on the basis of theoutput of the second magnetic sensor 9, the excitation switching timingfor the second magnetic pole section 7 a with respect to the rotationposition of the rotor 3 corresponds to an electrical advance anglebetween angle 45 degrees to 90 degrees.

FIGS. 16A to 16D are illustrations for describing positions in which thefirst magnetic sensor 8, the second magnetic sensor 9, the thirdmagnetic sensor 10, and the fourth magnetic sensor 11 are arranged. Asillustrated in FIGS. 16A to 16D, the first magnetic sensor 8 in themotor 1 according to the present embodiment is arranged in a positionthat satisfies the following conditions.

(a) In the clockwise driving, when the magnetized polarity of the firstmagnetic pole section 6 a is switched on the basis of the output of thefirst magnetic sensor 8, the excitation switching timing for the firstmagnetic pole section 6 a with respect to the rotation position of therotor 3 corresponds to an electrical advance angle between 0 degree and45 degrees (see FIG. 16A).

(b) In the counterclockwise driving, when the magnetized polarity of thefirst magnetic pole section 6 a is switched on the basis of the outputof the first magnetic sensor 8, the excitation switching timing for thefirst magnetic pole section 6 a with respect to the rotation position ofthe rotor 3 corresponds to an electrical advance angle between 45degrees and 90 degrees (see FIG. 16C).

The second magnetic sensor 9 in the motor 1 according to the presentembodiment is arranged in a position that satisfies the followingconditions.

(c) In the clockwise driving, when the magnetized polarity of the secondmagnetic pole section 7 a is switched on the basis of the output of thesecond magnetic sensor 9, the excitation switching timing for the secondmagnetic pole section 7 a with respect to the rotation position of therotor 3 corresponds to an electrical advance angle between 0 degree and45 degrees (see FIG. 16B).

(d) In the counterclockwise driving, when the magnetized polarity of thesecond magnetic pole section 7 a is switched on the basis of the outputof the second magnetic sensor 9, the excitation switching timing for thesecond magnetic pole section 7 a with respect to the rotation positionof the rotor 3 corresponds to an electrical advance angle between 45degrees and 90 degrees (see FIG. 16D).

The third magnetic sensor 10 in the motor 1 according to the presentembodiment is arranged in a position that satisfies the followingconditions.

(e) In the clockwise driving, when the magnetized polarity of the firstmagnetic pole section 6 a is switched on the basis of the output of thethird magnetic sensor 10, the excitation switching timing for the firstmagnetic pole section 6 a with respect to the rotation position of therotor 3 corresponds to an electrical advance angle between 45 degreesand 90 degrees (see FIG. 16A).

(f) In the counterclockwise driving, when the magnetized polarity of thefirst magnetic pole section 6 a is switched on the basis of the outputof the third magnetic sensor 10, the excitation switching timing for thefirst magnetic pole section 6 a with respect to the rotation position ofthe rotor 3 corresponds to an electrical advance angle between 0 degreeand 45 degrees (see FIG. 16C).

The fourth magnetic sensor 11 in the motor 1 according to the presentembodiment is arranged in a position that satisfies the followingconditions.

(g) In the clockwise driving, when the magnetized polarity of the secondmagnetic pole section 7 a is switched on the basis of the output of thefourth magnetic sensor 11, the excitation switching timing for thesecond magnetic pole section 7 a with respect to the rotation positionof the rotor 3 corresponds to an electrical advance angle between 45degrees and 90 degrees (see FIG. 16B).

(h) In the counterclockwise driving, when the magnetized polarity of thesecond magnetic pole section 7 a is switched on the basis of the outputof the fourth magnetic sensor 11, the excitation switching timing forthe second magnetic pole section 7 a with respect to the rotationposition of the rotor 3 corresponds to an electrical advance anglebetween 0 degree and 45 degrees (see FIG. 16D).

In the present embodiment, in consideration of errors in magnetizationof magnets, errors in dimensions of sensors, errors of yokes, eachmagnetic sensor is arranged in a range described below.

The first magnetic sensor 8 is arranged in a range where the excitationswitching timing for the first magnetic pole section 6 a in theclockwise driving corresponds to an electrical advance angle between14.4 degrees and 33.6 degrees and the excitation switching timing forthe first magnetic pole section 6 a in the counterclockwise drivingcorresponds to an electrical advance angle between 56.4 degrees and 75.6degrees.

The second magnetic sensor 9 is arranged in a range where the excitationswitching timing for the second magnetic pole section 7 a in theclockwise driving corresponds to an electrical advance angle between14.4 degrees and 33.6 degrees and the excitation switching timing forthe second magnetic pole section 7 a in the counterclockwise drivingcorresponds to an electrical advance angle between 56.4 degrees and 75.6degrees.

The third magnetic sensor 10 is arranged in a range where the excitationswitching timing for the first magnetic pole section 6 a in theclockwise driving corresponds to an electrical advance angle between56.4 degrees and 75.6 degrees and the excitation switching timing forthe first magnetic pole section 6 a in the counterclockwise drivingcorresponds to an electrical advance angle between 14.4 degrees and 33.6degrees.

The fourth magnetic sensor 11 is arranged in a range where theexcitation switching timing for the second magnetic pole section 7 a inthe clockwise driving corresponds to an electrical advance angle between56.4 degrees and 75.6 degrees and the excitation switching timing forthe second magnetic pole section 7 a in the counterclockwise drivingcorresponds to an electrical advance angle between 14.4 degrees and 33.6degrees.

The midpoint of a line segment connecting the first magnetic sensor 8and the third magnetic sensor 10 corresponds to the electrical advanceangle 45 degrees at the excitation switching timing for the firstmagnetic pole section 6 a. The midpoint of a line segment connecting thesecond magnetic sensor 9 and the fourth magnetic sensor 11 correspondsto the electrical advance angle 45 degrees at the excitation switchingtiming for the second magnetic pole section 7 a. This reduces variationsin driving characteristics between the clockwise driving and thecounterclockwise driving in the present embodiment.

The present embodiment uses a sensor unit in which the first magneticsensor 8 and the third magnetic sensor 10 constitute a single unit andthe second magnetic sensor 9 and the fourth magnetic sensor 11constitute a single unit. In this case, in the clockwise driving, thefirst magnetic sensor 8 is in the position where the excitationswitching timing for the first magnetic pole section 6 a corresponds tothe electrical advance angle 21 degrees, and the third magnetic sensor10 is in the position where the excitation switching timing for thefirst magnetic pole section 6 a corresponds to the electrical advanceangle 69 degrees. In the clockwise driving, the second magnetic sensor 9is in the position where the excitation switching timing for the secondmagnetic pole section 7 a corresponds to the electrical advance angle 21degrees, and the fourth magnetic sensor 11 is in the position where theexcitation switching timing for the second magnetic pole section 7 acorresponds to the electrical advance angle 69 degrees.

The present invention can provide a shutter device in which, when adriven member is driven by a stepping motor and thus a light shieldingmember moves from a closed state to an open state or from the open stateto the closed state, a stepping motor does not lose synchronization.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1. A shutter device comprising: a first shutter driving mechanismincluding a first motor, a first driven member configured to be drivenby the first motor, and a first light shielding member configured to bedriven by the first driven member so as to open or close an aperture; asecond shutter driving mechanism including a second motor, a seconddriven member configured to be driven by the second motor, and a secondlight shielding member configured to be driven by the second drivenmember so as to open or close an aperture; and a control unit configuredto control the first motor and the second motor, wherein in a case wherethe shutter device performs in a first-frame shooting operation, thecontrol unit controls the first motor and the second motor such that thefirst shutter driving mechanism performs an exposure operation prior toan exposure operation of the second shutter driving mechanism, andwherein in a case where the shutter device performs in a second-frameshooting operation directly after the first-frame shooting operation,the control unit controls the first motor and the second motor such thatthe second shutter driving mechanism performs an exposure operationprior to an exposure operation of the first shutter driving mechanism.2. The shutter device according to claim 1, wherein each of the firstand second driven members is configured to provide a first driven zone,a second driven zone and a third driven zone, wherein in a case wherethe first and second driven members are driven in the first driven zone,the first and second light shielding members maintain the closed stateor the open state, wherein in a case where the first and second drivenmembers are driven in the second driven zone, the first and second lightshielding member travel from the closed state to the open state or fromthe open state to the closed state, and wherein in a case where thefirst and second driven members are driven in the third driven zone, thefirst and second light shielding members maintain the closed state orthe open state.
 3. The shutter device according to claim 2, wherein thefirst motor is configured to be driven in open-loop driving mode atwhich an energization state of a first coil is switched at predeterminedtime intervals and in feed-back driving mode at which the energizationstate of the first coil is switched in accordance with a rotationposition of a first rotor, wherein in a case where the first drivenmember is driven in the first driven zone, the first motor drives thefirst driven member in the open-loop driving mode, wherein in a casewhere the first driven member is driven in the second or third drivenzone, the first motor drives the first driven member in the feed-backdriving mode, wherein the second motor is configured to be driven inopen-loop driving mode at which an energization state of a second coilis switched at predetermined time intervals and in feed-back drivingmode at which the energization state of the second coil is switched inaccordance with a rotation position of a second rotor, wherein in a casewhere the second driven member is driven in the first driven zone, thesecond motor drives the second driven member in the open-loop drivingmode, and wherein in a case where the second driven member is driven inthe second or third driven zone, the second motor drives the seconddriven member in the feed-back driving mode.
 4. The shutter deviceaccording to claim 1, wherein each of the first and second drivenmembers has a cam groove, wherein each of the first and second lightshielding members has a follower portion which follows the cam groove,wherein the cam groove has a first cam region, a second cam region and athird cam region, wherein in a case where the follower portion followsthe first cam region, each of the first and second light shieldingmembers maintains a closed state in which an aperture is closed or aopen state in which the aperture is open, wherein in a case where thefollower portion follows the a second cam region, each of the first andsecond light shielding members travels from the closed state to the openstate or from the open state to the closed state, and wherein in a casewhere the follower portion follows the third cam region, each of thefirst and second light shielding members maintains a closed state inwhich an aperture is closed or an open state in which the aperture isopen.
 5. The shutter device according to claim 4, wherein the firstmotor is configured to be driven in open-loop driving mode at which anenergization state of a first coil is switched at predetermined timeintervals and in feed-back driving mode at which the energization stateof the first coil is switched in accordance with a rotation position ofa first rotor, wherein in a case where the follower portion of the firstlight shielding member follows the first cam region of the first drivenmember, the first motor drives the first driven member in the open-loopdriving mode, wherein in a case where the follower portion of the firstlight shielding member follows the second or third cam region of thefirst driven member, the first motor drives the first driven member inthe feed-back driving mode, wherein the second motor is configured to bedriven in open-loop driving mode at which an energization state of asecond coil is switched at predetermined time intervals and in feed-backdriving mode at which the energization state of the second coil isswitched in accordance with a rotation position of a second rotor,wherein in a case where the follower portion of the second lightshielding member follows the first cam region of the second drivenmember, the second motor drives the second driven member in theopen-loop driving mode, and wherein in a case where the follower portionof the second light shielding member follows the second or third camregion of the second driven member, the second motor drives the seconddriven member in the feed-back driving mode.
 6. An image pickupapparatus comprising a shutter device, wherein the shutter devicecomprises: a first shutter driving mechanism including a first motor, afirst driven member configured to be driven by the first motor, and afirst light shielding member configured to be driven by the first drivenmember so as to open or close an aperture; a second shutter drivingmechanism including a second motor, a second driven member configured tobe driven by the second motor, and a second light shielding memberconfigured to be driven by the second driven member so as to open orclose an aperture; and a control unit configured to control the firstmotor and the second motor, wherein in a case where the shutter deviceperforms in a first-frame shooting operation, the control unit controlsthe first motor and the second motor such that the first shutter drivingmechanism performs an exposure operation prior to an exposure operationof the second shutter driving mechanism, and wherein in a case where theshutter device performs in a second-frame shooting operation directlyafter the first-frame shooting operation, the control unit controls thefirst motor and the second motor such that the second shutter drivingmechanism performs an exposure operation prior to an exposure operationof the first shutter driving mechanism.
 7. The image pickup apparatusaccording to claim 6, wherein each of the first and second drivenmembers is configured to provide a first driven zone, a second drivenzone and a third driven zone, wherein in a case where the first andsecond driven members are driven in the first driven zone, the first andsecond light shielding members maintain the closed state or the openstate, wherein in a case where the first and second driven members aredriven in the second driven zone, the first and second light shieldingmembers travel from the closed state to the open state or from the openstate to the closed state, and wherein in a case where the first andsecond driven members are driven in the third driven zone, the first andsecond light shielding members maintain the closed state or the openstate.
 8. The image pickup apparatus according to claim 7, wherein thefirst motor is configured to be driven in open-loop driving mode atwhich an energization state of a first coil is switched at predeterminedtime intervals and in feed-back driving mode at which the energizationstate of the first coil is switched in accordance with a rotationposition of a first rotor, wherein in a case where the first drivenmember is driven in the first driven zone, the first motor drives thefirst driven member in the open-loop driving mode, wherein in a casewhere the first driven member is driven in the second or third drivenzone, the first motor drives the first driven member in the feed-backdriving mode, wherein the second motor is configured to be driven inopen-loop driving mode at which an energization state of a second coilis switched at predetermined time intervals and in feed-back drivingmode at which the energization state of the second coil is switched inaccordance with a rotation position of a second rotor, wherein in a casewhere the second driven member is driven in the first driven zone, thesecond motor drives the second driven member in the open-loop drivingmode, and wherein in a case where the second driven member is driven inthe second or third driven zone, the second motor drives the seconddriven member in the feed-back driving mode.
 9. The image pickupapparatus according to claim 6, wherein each of the first and seconddriven members has a cam groove, wherein each of the first and secondlight shielding members has a follower portion which follows the camgroove, wherein the cam groove has a first cam region, a second camregion and a third cam region, wherein in a case where the followerportion follows the first cam region, each of the first and second lightshielding members maintains a closed state in which an aperture isclosed or an open state in which the aperture is open, wherein in a casewhere the follower portion follows the second cam region, each of thefirst and second light shielding members travels from the closed stateto the open state or from the open state to the closed state, andwherein in a case where the follower portion follows the third camregion, each of the first and second light shielding member maintains aclosed state in which an aperture is closed or an open state in whichthe aperture is open.
 10. The image pickup apparatus according to claim9, wherein the first motor is configured to be driven in open-loopdriving mode at which an energization state of a first coil is switchedat predetermined time intervals and in feed-back driving mode at whichthe energization state of the first coil is switched in accordance witha rotation position of a first rotor, wherein in a case where thefollower portion of the first light shielding member follows the firstcam region of the first driven member, the first motor drives the firstdriven member in the open-loop driving mode, wherein in a case where thefollower portion of the first light shielding member follows the secondor third cam region of the first driven member, the first motor drivesthe first driven member in the feed-back driving mode, wherein thesecond motor is configured to be driven in open-loop driving mode atwhich an energization state of a second coil is switched atpredetermined time intervals and in feed-back driving mode at which theenergization state of the second coil is switched in accordance with arotation position of a second rotor, wherein in a case where thefollower portion of the second light shielding member follows the firstcam region of the second driven member, the second motor drives thesecond driven member in the open-loop driving mode, and wherein in acase where the follower portion of the second light shielding memberfollows the second or third cam region of the second driven member, thesecond motor drives the second driven member in the feed-back drivingmode.